UPDATE: It took about half an hour for Fox to correct our earlier report that Avatar may have been pushed back, based on the release date on the official website disappearing. Turns out the release date is the same; it was just a glitch in the site's system. So no worries! Avatar is still set for a December 18, 2009 release. Below is the original story.

Release dates are fickle things, as everyone looking forward to the new Harry Potter movie learned this summer. And James Cameron's Avatar has had some particularly slippery release dates, given its reliance on incredibly complex technology and its plans to only be released in 3D, which many theaters aren't equipped for yet.

So while Avatar had been set for a Christmas 2009 release, it may have been pushed back yet again, as spotted by the guys at 3D tech blog Market Saw. They noticed that the official Fox Movies site has the date listed as "undefined," even though it had previously been December 18, 2009. They also point out that Anne Thompson, writing for Variety last month, suspected that Cameron would try to have the release pushed back to 2010.

At this point in Avatar's production and advertising process, it doesn't seem too late to push things back. And it would probably be a good thing, given all the technical challenges and the movie's reliance on 3D, which more and more movie theaters have installed but is by no means standard. Now we have to wait to see what Fox has to say about all this, and let us know whether or not this delay is actually happening.